1. Field of the Invention
The present invention relates generally to an ink-jet printing apparatus and an ink-jet printing method. More specifically, the present invention relates to an ink-jet printing apparatus and an ink-jet printing method, in which printing is performed by ejecting an ink and a liquid making a coloring agent in the ink insoluble.
2. Description of the Related Art
An ink-jet printing system is attracting attention in the recent years. The ink-jet printing system achieves a variety of advantages, such as the capability of high speed and high density printing, easiness of providing ability for color printing and making the apparatus compact, and so on. Examples of such system has been disclosed in U.S. Pat. Nos. 4,723,129 and 4,740,796.
In the ink-jet printing system, an ink which contains a water-soluble dye is typically used. Accordingly, when an image is formed on a printing medium, such as a plain paper, bleeding can be caused in the printed image by deposition of water droplets or the like, for example, due to insufficient water resistance of the dye fixed on the printing medium.
As a solution for this, an ink, in which water resistance is provided for the dye to be contained in the ink, has been used. However, it encounters problems to be solved, such as water resistance of the dye not being yet complete, and since such ink has a low solubility, it is possible to cause plugging of the ink in an ejection opening of a head and so on.
As another method for attaining water resistance, a method for improving water resistance of the image by preliminarily depositing a transparent liquid to make the dye insoluble (hereinafter referred to as "processing liquid") on the printing medium, such as a printing paper, has been developed. For example, in Japanese Patent Application Laid-open No. 63185/1989, there is disclosed a technology to eject and deposit the processing liquid by an ink-jet printing head. In the technology disclosed in the above-identified publication, a dot diameter of the processing liquid is set greater than a dot diameter of the printing ink. As a result, even when a deposited position of the processing liquid and a deposited position of the printing ink are mutually offset, desired characteristics can be obtained.
However, when using an ink and a transparent processing liquid to make a dye in the ink insoluble, setting the dot diameter of the processing liquid greater than the dot diameter of the ink, a necessary period for fixing the ink and the processing liquid on the printing medium becomes longer than a necessary period for fixing only ink. In this case, in a serial printer which performs printing by repeating scanning by a printing head, a current cycle of scanning of the printing head can be initiated before complete fixing of the processing liquid and the ink ejected in the immediately preceding cycle of scanning of the printing head. In the current cycle of scanning, if the processing liquid in a region located adjacent to a boundary of a printed region which has been printed in the immediately preceding scanning cycle, deposits to partly overlap with the processing liquid ejected in the immediately preceding scanning cycle, a deterioration of color can be caused in the boundary (joint portion) of the images formed per scan.
This problem is caused by separating the ink ejected on the processing liquid in the immediately preceding cycle of scanning by overlapping the processing liquid ejected in the current scanning cycle on the processing liquid deposited in the immediately preceding scanning cycle in the region adjacent to the boundary therebetween, to fix no coloring agent of the ink in the separated portion, if the current scanning cycle is performed before fixing of the processing liquid and the printed ink ejected in the immediately preceding scanning cycle.
Accordingly, this problem can be caused not only in the construction where the dot of the processing liquid is greater than that of the printing ink, but also in other constructions. Namely, even when the dot of the processing liquid is equal to or smaller than the dot of the printing ink, or when the dot of the processing liquid is formed with the processing liquid of an amount equal to or less than an amount of the printing ink, the foregoing problems can be caused. For example, when overlapping is caused in respective scanning regions due to registration error or another reason, a part of the dot of the processing liquid formed in the current scanning cycle may overlap with the dots of the processing liquid and the ink formed in the immediately preceding scan.
The foregoing influence of dot overlapping becomes more significant at greater ejection amounts of the processing liquid or at higher driving frequency of ejection. In this case, even if the dot diameter of the processing liquid is simply set to be greater than the dot diameter of the printing ink as described above, it is difficult to obtain desired characteristics when offset is caused in depositing positions of the processing liquid and the printing ink.